(i) FIELD OF THE INVENTION
The present invention relates to a device for sealing the shaft of a turbo machine.
(ii) DESCRIPTION OF THE PRIOR ART
A conventional device for sealing the shaft of a turbo machine will be described in reference to FIGS. 3 and 4 attached hereto.
Reference numeral 1 is a shaft of a turbo machine, and numeral 2 is a casing of the turbo machine. A seal sleeve 3 is disposed along the shaft 1 in a fluid-tight state, and an atmospheric side floating ring 4 and an in-machine side floating ring 5 are disposed surrounding the seal sleeve 3, on the side of the atmosphere and inside the machine, respectively. Onto the inner peripheral surfaces of the atmospheric side floating ring 4 and the in-machine side floating ring 5, a white metal 6 is applied. Ring-like lugs 4a, 4b provided on the atmospheric side edge portion of the atmospheric side floating ring 4 are in contact with a shaft sealing side plate 7 attached to the casing 2 in a fluid tight state. The atmospheric side floating ring 4 is engaged with a dowel pin 8 provided on the shaft sealing side plate 7, and a coiled spring 9 is received in a spring seat which is composed of both openings formed in confronted surfaces of the atmospheric side floating ring 4 and the in-machine side floating ring 5. A dowel ring 10 inserted into the coiled spring 9 is planted in the atmospheric side floating 4. The in-machine side floating ring 5 is partially in contact with a seal case 11 attached fluidtightly to the casing 2 in the in-machine side portion of the case 11, and the casing 2 and the seal case 11 have oil feed openings 2a and 11a, respectively. On the atmospheric side of the shaft sealing side plate 7, a casing cover 12 attached fluid-tightly to the casing 2 is provided with a labyrinth 13 surrounding the shaft 1.
By means of a spring force of the coiled spring 9, the lugs 4a, 4b of the atmospheric side floating ring 4 are in contact with the shaft sealing side plate 7 and the inmachine side floating ring 5 is in contact with the inner surface of the in-machine side portion of the seal case 11. When the turbo machine is driven, a seal fluid having a specified pressure which is a little higher than a fluid pressure in the turbo machine to be sealed flows through the oil feed openings 2a and 11a in a direction shown by an arrow B in FIG. 3 and is then divided into two streams. One of these streams flows through a space between the seal sleeve 3 and the in-machine side floating ring 5 and returns to a seal fluid tank. At this time, the seal fluid serves to seal portions occupied by the fluid in the turbo machine and to lubricate the region between the white metal 6 of the in-machine side floating ring 5 and the seal sleeve 3. In this case, since the in-machine side floating ring 5 is pressed toward the inside of the machine, the seal case 11 is brought into contact with the in-machine side floating ring 5 at the contact portion thereof, as described above. However, even if a small space is present at the contact portion owing to, for example, a working error, the flowing seal fluid will seal the small space thereat.
The other of the two streams above flows through a space between the seal sleeve 3 and the white metal 6 of the atmospheric side floating ring 4 and through the space on an inside surface of the labyrinth 13 attached to the casing cover 12, and returns to a seal fluid tank. At this time, the seal fluid serves to lubricate the space between the white metal 6 and the seal sleeve 3 and to seal the space therebetween so as to prevent the atmosphere from penetrating in therethrough. The atmospheric side floating ring 4 is strongly pressed toward the atmospheric side and the lugs 4a, 4b are pressed against the shaft sealing side plate 7, as described above. However, even if a small space is present between the lugs 4a, 4b and the plate 7, the seal fluid will flow therethough in order to seal therebetween and to thereby prevent the atmosphere from coming in therethrough.
When the shaft 1 is deformed due to the change in a load condition or a vibration, the atmospheric side floating ring 4 slides on the shaft sealing side plate 7 with the interposition of the lugs 4a, 4b, and the in-machine side floating ring 5 slides on the contact portion with the seal case 11. Since the atmospheric side floating ring 4 is engaged with the shaft sealing side plate 7 with the aid of the dowel pin 8 and since the in-machine side floating ring 5 is connected to the atmospheric side floating ring 4 via the dowell 10, the shaft sealing side plate 7 does not follow the deformation of the shaft 1.
However, in the case of the device for sealing the shaft of the turbo machine shown in FIGS. 3 and 4, a pressure P of the seal liquid acts on the in-machine side surface of the shaft sealing side plate 7 and the outer peripheral surface of the atmospheric side floating ring 4, as shown in FIG. 5. In addition thereto, the atmospheric pressure also acts on the atmospheric side surface of the shaft sealing side plate 7, and an inclinedly distributed pressure acts on the surface of the white metal 6 of the atmospheric side floating ring 4. That is to say, the atmospheric pressure is applied onto the surface end portion on the atmospheric side of the white metal 6 of the atmospheric side floating ring 4, and the pressure P of the seal liquid is applied onto the surface end portion on the in-machine side of the same 6. Therefore, a bending mement (Mb) acts on the shaft sealing side plate 7, and the latter 7 bends in a direction of this moment Mb and the atmospheric side floating ring 4 bends in a direction of a momemt Ma under the influence of the moment Ma generated by the action of a pressure Po which is a differential pressure between both the above pressures on the surface of the white metal 6. As a result, the shaft sealing side plate 7 is brought into contact with the atmospheric side floating ring 4 via an outer edge portion of the lug 4a as shown in FIG. 6, with the result that a contact area diminishes remarkably and a contact pressure increases noticeably. In consequence, the slide of the atmospheric side floating ring 4 on the shaft sealing side plate 7 is obstructed, and thus the atmospheric side floating ring 4 cannot follow the deformation of the shaft 1. For this reason, a surface pressure between the white metal 6 and the seal sleeve 3 is increased excessively, whereby hardening and scalling loss take place on the white metal 6 and the seal sleeve 3.